Bare Metal Prep.

O

Outlaw

Prior to SPI Epoxy, best prep is 80 Grit with DA sander followed by wiping with waterbourne 700 then solvent based 710 (Updated).

After filler or 2k, surface is final sanded with 180 prior to adding more epoxy for seal coat. Any sandthrus to bare metal would require a 80 grit scratch in the sand thru to bare metal only?

If a sand thru to bare metal in the middle of a area with 2k primer (finished with 180), is re shot with epoxy over 80 grit scratch, does the whole panel need another full skim coat of 2k primer to be reblocked with the sand thru?
 
I think the answer is no on both counts. Generally, we want large areas of bare metal to be in 80 or have a good blast profile to aid adhesion, but small sand-throughs in a 180 scratch are not a serious concern, if they have been cleaned carefully and get a good coat of epoxy.

My concern from what you wrote is that you indicate that 180 grit would be ready for sealer, and that would not normally be the case. 180 scratches are generally followed by a final primer application and re-blocked into 320 or finer, after which the substrate could be considered sealer-ready.
 
My oversight crash, I got a step ahead of myself. Not sure what I was thinking when I wrote that. I know better. I mainly wanted to know about very small sandthrus to bare metal and whether or not they had to be resanded with 80 grit in those spots. I have been just doing the 180 grit but wondered if I was doing it correctly. I have not sprayed any sealer yet do I will be sure and prep that with 320 or finer before I do. Thanks.
 
If those bare metal spots are big enough to sand with 80 grit then you may have areas of metal that is too high, or need more primer and blocking---just a thought.
 
I've, at times, broken through the 2K primer surfacer while blocking near rolled door edges and would just spot epoxy using a touch-up gun and a 1.0 mm tip over a 180 grit scratch. That small tip size gives an exceptionally smooth coat. I'll then spray on a coat or two of primer surfacer and carefully scuff sand it into the surroundings. I don't sand those exposed areas with 80 grit at the blocking stage. I've been told that I could spray unreduced epoxy into small areas up to 400 grit.

Mike
 
chevman;n85542 said:
If those bare metal spots are big enough to sand with 80 grit then you may have areas of metal that is too high, or need more primer and blocking---just a thought.
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Thanks Chevy, the bare spots are very small and barely show thru. Just places where I did not seem them in time to stop from going to bare metal.
 
Great input, the bare spots are very small and very few. I try to stop before I hit bare metal.
 
It makes it easier to know when to stop sanding by using a darker color epoxy under the primer surfacer. Or a lighter epoxy under a darker primer surfacer.

Mike
 
finally powdercoated some railings after I cleaned them with ospho, kept wiping until the white haze was gone. Nice iridescent pretreatment reaction to standard rectangular tubing.
 
That makes sense Mike, I have been trying to apply that but I have a lifetime of thinking that also means rock chips will show worse. But in reality, I think the paint will chip clear to filler or metal so it really dont matter in the primer buildup.
 
MikeS;n85543 said:
I've, at times, broken through the 2K primer surfacer while blocking near rolled door edges and would just spot epoxy using a touch-up gun and a 1.0 mm tip over a 180 grit scratch. That small tip size gives an exceptionally smooth coat. I'll then spray on a coat or two of primer surfacer and carefully scuff sand it into the surroundings. I don't sand those exposed areas with 80 grit at the blocking stage. I've been told that I could spray unreduced epoxy into small areas up to 400 grit.

Mike
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Mike, when you spray the small snd thrus with epoxy and then with one or two coats of primer surfacer and carefully scuff sand into the surroundings, dont you in theory end up with a "high spot" that will come thru the final finish? I have it in my head that the entire panel would have to be re-primed and block sanded to avoid a flaw (hump for lack of better words) in the final finish.
 
Once you have the SPI Turbo, SPI 2K or SPI 2K high build applied, do you block with 180 and then remove those scratches with 340/400 before sealer? Is the process different with black or dark colored base coats? Im thinking 400 for light colors or non metallic, but up to 600 for dark or metallic. Question is specific to Base/Clear.
 
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